The development of plastic blood collection bags in the 1960's facilitated the separation of donated whole blood into its various components, thereby making a platelet concentrate (PC) available as a transfusion product. A typical unit of random-donor PC is about 50 ml, and is typically produced from a unit of whole blood, which is about 450 ml in United States practice, by differential sedimentation.
The need for specific blood components is growing rapidly as the therapeutic administration of these components increases. The net result is twofold: biological fluids are increasingly important, and the need to maximize yield has increased. Thus, any amount that is retained in the processing system, or is recovered but is not viable and physiologically active, represents a potentially significant loss. While the failure to maximize yield is a serious concern with respect to all blood components, it is particularly applicable to the production of PC, since typical procedures for processing platelet containing solutions such as PC fail to efficiently maximize platelet recovery.
Maximizing recovery of platelets or a platelet concentrate after processing may be adversely affected in several ways. For example, platelets are notorious for being "sticky", an expression reflecting the tendency of platelets suspended in blood plasma to adhere to any non-physiological surface (e.g., the surfaces of the components of a system for processing biological fluid) to which they are exposed. Under many circumstances, they also adhere strongly to each other.
As detailed in U.S. Pat. No. 4,880,548, which discloses methods and devices for leucocyte depleting blood components including PC, there will be substantial contact between platelets and the internal surfaces of the leucocyte depletion device. It is therefore desirable that the leucocyte depletion device should minimize platelet loss due to that contact and should not adversely affect, platelet viability or physiological activity.
This problem is magnified when multiple units of platelet containing solutions are pooled or processed. When multiple Units of PC from random donors are pooled for transfusion into a patient, some of the fluid is trapped or retained in the individual collection and processing assemblies, collectively representing a significant loss if the highly valuable fluid can not be recovered.
In view of this, there is a growing need for a system and method for economically and efficiently processing a biological fluid, such as a platelet containing solution, that will not only pool large amounts (e.g. multiple units) of the fluid, but will also leucocyte deplete the fluid and maximize the recovery of platelets.